(a) Field of the Invention
The present invention relates to a method for charging battery of a hybrid vehicle at neutral shift range and a hybrid vehicle using the same generating electric energy and charging battery at a neutral shift range by restricting a rotation of an output element of the automatic transmission.
(b) Description of the Related Art
Typical hybrid vehicle has an automatic transmission having a planetary gear set consisting of a sun gear, a pinion gear, a planet carrier, and a ring gear.
In the planetary gear set, the sun gear is connected with a generator, the planet carrier is connected with an engine, and the ring gear is connected with a drive motor.
In the typical hybrid vehicle having such a structure, the engine is stopped at a neutral (N) shift range.
However, when the battery SOC (state-of-charge) is lower than predetermined lower limit, the engine is operated so as to charge the battery with a warning that the battery should be charged.
Here, the planet carrier is rotated by the engine, the ring gear is fixed by the weight of the vehicle, and the sun gear is freely rotated without any load. That is, a driving torque of the engine does not operate the generator.
Therefore, in this case, an engine rpm does not increase even though the driver kicks the accelerator pedal at the neutral (N) shift range.
If the engine rpm increases when the driver kicks the accelerator pedal at the neutral (N) shift range, a rotational speed and a torque of the planet carrier increases, and vehicle becomes run due to such a structure that cannot prevent power delivery to the wheel for running vehicle.
That is, if the engine is operated at the neutral (N) shift range so as to generate an electric power by operating the generator, the driving torque of the engine is delivered to the wheel through the ring gear, and vehicle runs. Therefore, according to the conventional hybrid vehicle, generating is prohibited at the neutral (N) shift range
Referring to a shift diagram of FIG. 1, the reason that generation is prohibited may be readily understood.
A left speed diagram of FIG. 1 shows rotational speeds of operational elements in the planetary gear set when an electric power is not generated, and a right speed diagram of FIG. 1 shows rotational speeds of operational elements in the planetary gear set when an electric power is generated.
Referring to the left speed diagram of FIG. 1, the ring gear acts as a fixed element, and sun gear has no load because the generation is not performed.
However, if generation is occurred in such a condition, the sun gear connected with the generator becomes under the load, and accordingly the ring gear becomes under the load, as shown in the right speed diagram of FIG. 1. Therefore, the vehicle starts to run.
Due to such a problem, the conventional hybrid vehicle cannot generates an electric power at the neutral (N) shift range. Therefore, when an air conditioner or various ramps are excessively used, main battery may be discharged. In addition, a torque of engine cannot be efficiently used at the neutral (N) shift range.
The information set forth in this Background of the Invention section is only for enhancement of understanding of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.